The present invention relates to the field of digital rock physics and, more particularly, to methods of preparing sample-embedded slivers which can be more efficiently and accurately analyzed. The present invention further relates to systems for performing the methods, and an x-ray scannable sliver product which can integrate a sample alone or together with reference objects into a stabilized single unit for handling and x-ray scanning.
Samples of rock obtained from a drilled well have been used to obtain estimates of rock composition and properties such as permeability, porosity, elasticity and other properties, and so forth, which are typical of an entire subterranean rock formation or facies. These estimates can have substantial significance, such as for characterizing the economic value of reservoir rock formations.
One common sample used to estimate rock properties is a well core. Well cores are very small compared to an entire formation, so multiple well cores are typically taken and analyzed and rock properties are interpolated in between geographic locations of the cores. Nevertheless, cores can be approximately a meter in length and 1/10 meter in diameter. Laboratory analysis of rock samples such as cores can be difficult and time consuming, and typically must be done off-site. Cores must be extracted and shipped to a laboratory for analysis and this can require many days or weeks to complete. Further, physical lab experiments are difficult to perform due to the usual size and shape of well samples such as cores, and the need to use sufficiently large sized samples to obtain accurate results by laboratory analysis.
Devices for generating digital images of rock samples are available for use. These devices include, for example, computer tomographic (CT) devices, scanning electron microscopy (SEM) devices, and FIB-SEM (focused ion beam combined with SEM) devices. Digital rock physics techniques for estimating rock properties have the advantage that they can accurately scan and produce digital images of very fine pore structures and they can identify small volumes of organic materials present in the pore structure of the rock. However, it is very time consuming and expensive to digitally scan very large samples to estimate rock properties. For example, shales can have an average pore size of about 0.005 to 1.0 μm and a well core typically can be about 100,000 μm (0.1 m) in diameter and 1,000,000 μm (1 m) or more in length. Scanning the entire sample at a resolution high enough to identify all of the pores can result in a complete assessment of the pore structure of the sample. However, scanning the entire sample at a resolution high enough to identify all of the pores is not practical due to the time and expense required to do a complete scan.
The present investigators have recognized that if samples of rock are machined down to relatively smaller and thinner dimensions in attempts to overcome the indicated shortcomings of large samples that the physical ability of the smaller sample to tolerate and withstand typical forces associated with machining can be a problem. For example, the present investigators recognized that looser consolidated rock or other types of samples may not be able to physically tolerate machining and other processing and handling used on the sample to prepare it for CT, SEM, or FIB-SEM analysis. The present investigators have further recognized that attempts to stabilize the sample with an integrally attached backing before machining that would still be retained as an attachment at the time of subsequent x-ray projection of the sample can cause interference problems and impair results.